Acoustic glass breakage detectors are used in security systems for homes and other structures to detect an attempt by an intruder to enter the structure by breaking a pane of glass such as found in a window or a glass door. Such detectors are normally installed inside the structure so that an intruder cannot disable or disarm them from outside the structure.
Most such detectors work by using a microphone to detect acoustic information or sounds, analyzing the sounds to extract a reduced set of significant parameters, and comparing the values of that set of parameters against the values of a set of predetermined glass break parameters that correspond to a glass breakage event. If the values of the set of significant parameters have a predetermined relationship with the values of the set of predetermined glass breakage parameters, a signal is generated to a central alarm control panel, which then generates an alarm (as an example, a siren) audible locally at the structure and/or a remote alarm (as an example, an alarm signal transmitted by telephone or radio). Sounds for which the values of the set of significant parameters do not have the predetermined relationship with the values of the set of predetermined glass breakage parameters do not lead to an alarm signal.
A home or business owner ordinarily can set the control panel to arm or disarm a glass breakage detector. Historically, control panels have been set to arm such a detector only in a structure that is not occupied by people and therefore is relatively quiet. As an example, such a detector has typically been armed to protect a business only when all employees have left, and the business has closed, for the night.
It would be desirable to arm an acoustic glass breakage detector to protect a person legitimately present in a structure from possible harm caused by an intruder. A locally audible alarm triggered by a glass breakage event could deter an intruder and could warn the legitimate occupant. The glass breakage event could also be signalled to a remote location so that authorities can be called to the structure.
Unfortunately, acoustic glass breakage detectors of the types now commercially available are not able to distinguish many common household or business sounds from true glass breakage events. Serious problems are caused by false alarms when such a detector is armed to protect a structure having a legitimate occupant. Thus, such a detector is typically not armed when someone is legitimately present in a structure to be protected because the risk of false alarms is intolerably high.